Correction to This Article
An April 17 A-section article and this article referred to government statements that 90 percent of guns seized from narco-traffickers in Mexico are traced to the United States. U.S. officials say 90 percent of weapons submitted to the United States for tracing originate in this country.

President Obama yesterday ratcheted up efforts to curb the flow of drugs and guns across the southern border, imposing financial sanctions against three of the most violent Mexican drug cartels and threatening to prosecute Americans who do business with them.

On the eve of his summit with Mexican President Felipe Calderón today, Obama added the cartels to the list of banned foreign "drug kingpins," a move that empowers the federal government to seize their assets, estimated to be in the billions of dollars. It also allows the government to seek criminal penalties against U.S. firms or individuals who provide weapons, launder money or transport drugs or cash for the organizations.

By targeting the cartels -- Sinaloa, Los Zetas and La Familia Michoacana -- the administration expanded its support for Calderón's crackdown on the narco-traffickers, an effort that has provoked a violent backlash and led to thousands of deaths in the past two years.

The Obama administration accelerated what is normally a year-long effort to add names to the banned list. The government did not identify assets held by the three cartels, but authorities have estimated that $19 billion to $39 billion in drug proceeds flows south each year from the United States.

The financial sanctions provide an additional tool against the organizations, whose drug and gun trafficking has proved exceedingly difficult to curtail. Mexico, for example, has seized more than 35,000 firearms from narco-traffickers since December 2006, and both governments say 90 percent of the weapons originated in the United States.

The effort to curb the southbound flow of what some have called an "iron river of guns" has faced heavy obstacles, including limited resources, relatively open access to firearms and political opposition to tighter gun regulation.

Even if the supply of U.S. guns were cut off, as long as the flow of money to the cartels continues, they could rearm by buying from other countries, including those in Eastern Europe or Central America, where surplus weapons from conflicts in the 1980s remain, analysts said.

"It's convenient for the cartels to be able to shop in Arizona, New Mexico, Texas and elsewhere," said George W. Grayson, a Mexico scholar at the College of William and Mary and author of the monograph "Mexico's Struggle With 'Drugs and Thugs.' " But stopping the U.S. trade, he said, would merely place "a thorn in the side of the cartels, rather than an AK-47 in the heart."

Since 2000, 78 drug kingpin groups and individuals have been blacklisted by the U.S. government, along with nearly 500 others who have supported them. The law has been used most extensively against Colombian drug traffickers, particularly the Cali cartel.

A Treasury Department official said its office of foreign assets control is working with other agencies to identify cartel assets, but the official described a much broader net of potential liability. Anyone who knowingly deals with a cartel representative or provides goods, services or other support can face penalties, the official said, including money launderers, front companies and other facilitators. That could include banks and other financial institutions, gun dealers, money-transfer companies and transportation firms.

"If you are a Mexican company buying or receiving weapons for a cartel, you can be designated," the official said. "If you are the U.S. person selling or transporting those weapons to the cartel or any [other] designated targets, you can be fined civilly and criminally prosecuted, or both."

Julie L. Myers, a former Justice Department official who led Immigration and Customs Enforcement until last fall, said kingpin designations have been powerful tools against Colombian drug cartels, in some cases persuading defendants to agree to plea deals to protect family assets.